We are developing new nanomaterials with novel properties for electronics, optics, and photoelectronics applications. Due to unique features in structure, these nanomaterials show performance better than bulk materials by, for example, providing large surface area and better electrical transport, or generating quantum confinement effect and photonic localization effect. These advantages of nanomaterials have resulted in potential applications in energy harvesting and storage, photocatalyst, hydrogen generation, and chemical sensors. One of the highlights of our recent research is that the efficiency of dye-sensitized solar cells has been improved by more than twice through employing a kind of new nanostructure, so-called aggregates of nanocrystallites, to replace the nanoparticles used in conventional photoelectrode films. This technology is anticipated to be also effective in enhancing optical absorption and thus the conversion efficiency of other types of solar cells. Our current work is also aiming to extend such nanostructure for lithium ion battery and photocatalyst application.